We propose X-ray crystallographic structural studies of the envelope glycoproteins from HIV, the virus that cause AIDS. A long-range goal is to use structural information about receptor- binding, fusion activity and antigenicity to design inhibitors and to improve potential vaccines. The project requires definition of stable, well-folded species for rational crystallization efforts. Important information about the properties of the gp120-gp41 complex will be obtained in such experiments. We will begin with secreted gp120 and membrane-bound gp160 from genetically engineered mammalian and insect-cell vectors. We will seek to prepare a soluble (i.e., membrane-anchorless) form of gp160 or of gp120-gp41 by genetic deletion and by limited proteolysis. We will examine glycoproteins derived from several isolates of HIV, and we will explore the effect of carbohydrate content by using glycosidase-treated and genetically-engineered carbohydrate deficient proteins. We will search for a minimum T4 binding domain, using limited proteolysis and end-deletion mutagenesis of secreted gp120, since preparation of such a domain might facilitate study of virus-receptor interaction, including crystallization of a complex with soluble T4. We will determine the oligomeric state, proteolytic susceptibility, T4 binding, antibody binding, and membrane-fusion activity of all forms of the glycoprotein to be crystallized, and we will compare these properties with those of native glycoprotein (gp120-gp41) from stably infected, non-virus-producing cells.